(19)
(11) EP 0 895 229 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
23.02.2000 Bulletin 2000/08

(43) Date of publication A2:
03.02.1999 Bulletin 1999/05

(21) Application number: 98113995.9

(22) Date of filing: 27.07.1998
(51) International Patent Classification (IPC)7: G11B 7/095, G11B 7/125
(84) Designated Contracting States:
AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE
Designated Extension States:
AL LT LV MK RO SI

(30) Priority: 31.07.1997 JP 20579497

(71) Applicant: Hitachi, Ltd.
Chiyoda-ku, Tokyo 101-8010 (JP)

(72) Inventors:
  • Kimura, Katsuhiko
    Niihari-gun, Ibaraki-ken (JP)
  • Yamauchi, Yoshiaki
    Higashiibaraki-gun, Ibaraki-ken (JP)
  • Kato, Seiichi
    Niihari-gun, Ibaraki-ken (JP)
  • Watanabe, Naruo
    Niihari-gun, Ibaraki-ken (JP)

(74) Representative: Beetz & Partner Patentanwälte 
Steinsdorfstrasse 10
80538 München
80538 München (DE)

   


(54) Tilt detection method and optical disk drive


(57) In an optical disk drive using as a light source a semiconductor laser (20) having a main electrode (30) and a plurality of subsidiary electrodes (31, 32), a wave front of a generated laser beam is modulated by controlling injection currents to the plurality of subsidiary electrodes, in accordance with a change in signal outputs when the wave front is modulated, a tilt is detected between a direction normal to the surface of an optical disk (9) and an objective lens optical axis, and in accordance with the detected tilt, the injection currents to the semiconductor laser are determined to correct the tilt. Since the tilt is detected and corrected through electrical modulation, the system can be made compact without using new components for tilt detection, and high speed control up to a high frequency becomes possible because there is no limit of the control bandwidth to be caused by sub-resonances in a high frequency band, like a mechanical actuator.






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